1. Technical Field
This invention relates to high definition television systems and more particularly, to an apparatus and method for recording and reproducing high definition video information arranged for display on a high definition television system.
2. Description of the Prior Art
There is an increasing interest in high definition television (HDTV). Indeed, it is widely anticipated that some form of HDTV will be the next major advance in television broadcasting. In a "high definition" telecast, images will be transmitted with much greater resolution than is currently provided under the standard National Television System Committee (NTSC) system. The current thinking is that HDTV in the United States will offer approximately six times as much information per frame than is currently transmitted. If no changes are made in the manner of forming the television signals, that would mean, of course, a six fold increase in the bandwidth required for transmitting the HDTV signal.
Conventional Television signals that are broadcast terrestrially occupy government-specified frequency channels. There is essentially no unused frequency bandwidth that can be devoted to HDTV signals except, perhaps, for the guard bands that are currently provided between adjacent NTSC TV channels. The guard bands are included in the spectrum allocation scheme to reduce the potential interference between the signals of adjacent channels. The interference might occur by virtue of unavoidable transmission into frequency bands outside the band specified for the transmitter, and/or undue reception by the receiver of signals from outside the band specified for the receiver. The challenge for HDTV designers, therefore, is to compress the HDTV signal, to communicate the compressed signal to a receiver within the available bandwidth, and to uncompress the signal within the receiver and restore to its original form, without undue degradation.
A number of techniques have been proposed in the art for reducing the bandwidth of TV images. Typically, these techniques reduce bandwidth by encoding the video signals, identifying redundancies in the encoded signals, and extracting the redundant signals in such a way that the original signal can be reconstituted by the receiver. Feasibility studies based on such bandwidth reduction techniques are currently under consideration along with the development of video tape recorders (VTRs) capable of recording and reproducing these HDTV video signals.
One such HDTV system currently under consideration is called "Digital Spectrum Compatible" (DSC)-HDTV and provides full high-definition resolution-perceived to be equal to the studio original- even after compressing the wide bandwidth signal into a 6-MHz channel. The DSC-HDTV system is described in a number of commonly assigned United States Patents. These are: U.S. Pat. No. 5,083,206 which issued to S.C. Knauer et al. on Jan. 21, 1992 and is entitled A High Definition Arrangement Including Noise Immunity Means; U.S. Pat. No. 5,063,444 which issued to S. C. Knauer et al. on Nov. 5, 1991 and is entitled A High Definition Television Arrangement with Signal Selections Adapted to the Available Transmission Capacity; U.S. Pat. No. 5,148,274 which issued to S.C. Knauer et al. on Sep. 15, 1992 and is entitled PAM Signal Modulation with Mappings to Improve Utilization of Available Transmission Capacity; and U.S. Pat. No. 5,134,475 which issued to J. D. Johnston et al. on Jul. 28, 1992 and is entitled An Adaptive Leak HDTV Encoder.
The DSC-HDTV system digitally transmits the compressed signal on currently unusable TV channels with only a minimum interference to or from NTSC channels. the DSC-HDTV system is compatible with other media, including cable, satellite, studio and home VTRs, video disc and fiber. Because the complete high-definition television signal (including video, chroma, audio, ancillary signals, decoder address, and encryption information) is encoded into one 6-MHz bandwidth signal, the system can be often adapted for use in the above mentioned TV signal applications.
In connection with the VTR application, however, some problems do arise. That is, while under normal conditions of playback, conventional VTRs will properly read video signals recorded in the DSC-HDTV system. When attempting to read these signals in special modes such as fast forward or fast reverse, problems occur in the decoding of the data representative of these video signals. It is therefore desirable to provide a VTR which is able to decode recorded DSC-HDTV signals without these limitations on the playback of information.